a, 9x+5-(x+20)=4(x+20)+2 b,5(x-6)=20(x-5)+2(x+30)

Đáp án:

`a,`

`9x + 5 – (x + 20) = 4 (x + 20) + 2`

`⇔ 9x + 5 – x – 20 = 4x + 80 + 2`

`⇔ (9x – x) + (5 – 20) = 4x + (80 + 2)`

`⇔ 8x – 15 = 4x + 82`

`⇔ 8x – 4x = 15 + 82`

`⇔ (8 – 4)x = 97`

`⇔ 4x = 97`

`⇔ x = 97 ÷ 4`

`⇔ x  =97/4`

`text{Vậy}` `x = 97/4`

`b,`

`5 (x – 6) = 20 (x – 5) + 2 (x + 30)`

`⇔ 5x – 30 = 20x – 100 + 2x + 60`

`⇔ 5x – 30 = (20x + 2x) + (-100 + 60)`

`⇔ 5x-30=22x – 40`

`⇔ 5x – 22x = 30 – 40`

`⇔ (5 – 22)x = -10`

`⇔ -17x = -10`

`⇔ x = -10 ÷ (-17)`

`⇔ x = 10/17`

`text{Vậy}` `x = 10/17`